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Wireless Security

Learn about the critical security issues in 802.11 wireless networks, the risks of using WEP encryption, and how attackers exploit vulnerabilities. This talk covers the history, flaws, and future directions in wireless security.

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Wireless Security

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  1. Wireless Security David Wagner University of California, Berkeley

  2. The Setting An example of a 802.11 wireless network (current installed base in the millions of users) Internet

  3. The Problem: Security! • Wireless networking is just radio communications • Hence anyone with a radio can eavesdrop, inject traffic

  4. WEP • The industry’s solution: WEP (Wired Equivalent Privacy) • Share a single cryptographic key among all devices • Encrypt all packets sent over the air, using the shared key • Use a checksum to prevent injection of spoofed packets (encrypted traffic)

  5. Why You Should Care

  6. More Motivation

  7. Overview of the Talk • In this talk: • Security evaluation of WEP • The history, where we stand today,and future directions

  8. 1997 802.11 WEP standard released Simon, Aboba, Moore: some weaknesses Mar 2000 Walker: Unsafe at any key size Oct 2000 Jan 30, 2001 Feb 5, 2001 Borisov, Goldberg, Wagner: 7 serious attacks on WEP NY Times, WSJ break the story Early History of WEP

  9. checksum RC4 key IV encrypted packet How WEP Works IV original unencrypted packet

  10. A Property of RC4 • Keystream leaks, under known-plaintext attack • Suppose we intercept a ciphertext C, and suppose we can guess the corresponding plaintext P • Let Z = RC4(key, IV) be the RC4 keystream • Since C = P Z, we can derive the RC4 keystream Z byP C = P (P Z) = (P P)  Z = 0 Z = Z • This is not a problem ... unless keystream is reused!

  11. A Risk With RC4 • If any IV ever repeats, confidentiality is at risk • Suppose P, P’ are two plaintexts encrypted with same IV • Let Z = RC4(key, IV); then the two ciphertexts areC = P Z and C’ = P’  Z • Note that C C’ = P P’,hence the xor of both plaintexts is revealed • If there is redundancy, this may reveal both plaintexts • Or, if we can guess one plaintext, the other is leaked • So: If RC4 isn’t used carefully, it becomes insecure

  12. Attack #1: Keystream Reuse • WEP didn’t use RC4 carefully • The problem: IV’s frequently repeat • The IV is often a counter that starts at zero • Hence, rebooting causes IV reuse • Also, there are only 16 million possible IV’s, so after intercepting enough packets, there are sure to be repeats • Implications: can eavesdrop on 802.11 traffic • An eavesdropper can decrypt intercepted ciphertexts even without knowing the key

  13. Attack #2: Spoofed Packets • Attackers can inject forged traffic onto 802.11 nets • Suppose I know the value Z = RC4(key, IV) for some IV • e.g., by using the previous attack • This is all I need to know to encrypt using this IV • Since the checksum is unkeyed, I can create valid ciphertexts that will be accepted by the receiver • Implication: can bypass access control • Can attack any computer attached to the wireless net

  14. Summary So Far • None of WEP’s goals are achieved • Confidentiality, integrity, access control all broken • And these are only 2 of the 7 attacks we showed in our paper…

  15. Mar 2001 Arbaugh: Your 802.11 network has no clothes Arbaugh: more attacks … May 2001 Jun 2001 Newsham: dictionary attacks on WEP keys Aug 2001 Fluhrer, Mantin, Shamir: efficient attack on way WEP uses RC4 Arbaugh, Mishra: still more attacks Feb 2002 Subsequent Events Jan 2001 Borisov, Goldberg, Wagner

  16. Evaluation of WEP • WEP cannot be trusted for security • Attackers can eavesdrop, spoof wireless traffic • Can often break the key with a few minutes of traffic • Attacks are very serious in practice • Attack tools are available for download on the Net • Hackers sitting in a van in your parking lot may be able to watch all your wireless data, despite the encryption

  17. To find wireless nets: Load laptop, 802.11 card, and GPS in car Drive While you drive: Attack software listens and builds map of all 802.11 networks found War Driving

  18. War Driving: Chapel Hill

  19. Driving from LA to San Diego

  20. Zoom in on Los Angeles

  21. Example: RF Leakage

  22. One Network in Kansas City

  23. Silicon Valley

  24. San Francisco

  25. Toys for Hackers

  26. A Dual-Use Product

  27. Conclusions • Wireless networks: insecure in theory & in practice • 50-70% of networks never even turn on encryption, and the remaining are vulnerable to attacks shown here • Hackers are exploiting these weaknesses in the field, from distances of a mile or more • Lesson: Open design is important • These problems were all avoidable • In security-critical contexts, be wary of wireless!

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